In many applications a plurality of commercial off-the-shelf (COTS) or modifiable off-the-shelf (MOTS) packaged power supply modules or “bricks” may be connected in parallel to support systems requiring supplied load currents that are larger than the capabilities of each individual module. The output voltage of each packaged module is typically controlled by internal control circuitry, which may include an error amplifier. In the event of an increase in the load current demand, the output voltage of the supply decreases. This internal error amplifier senses the voltage decrease through its external remote voltage sense terminals or pins, and drives the module output voltage higher, restoring a desired output voltage level at the new output load current. As typical COTS and MOTS modules have their control circuitry isolated by potted materials, these remote sense terminals are the only means available to change the feedback of the internal control loops of the modules.
When arranged in parallel configurations, the modules often do not provide equal output current (i.e. where each of N modules provides the load current/N). This may be the result of, for example, the tolerances of the internal voltage references and resistor dividers within each module causing each module to settle to a slightly different output voltage during use. Moreover, when these modules have their outputs connected in parallel, the modules with the highest output voltage will attempt to supply the load current. The other modules, with lower level output voltages, will sense that the output voltage already exceeds their set point levels so they do not have to supply anything. The result may be that only a small number of modules provide all of the load current while a remaining portion of the modules supply little or no current. As certain applications require that each module supply an equal share of the load current, some feedback method must be implemented to achieve improved output balance during operation.
Accordingly, improved systems and methods are desired for providing even current sharing between parallel COTS power supplies for balancing the outputs thereof.